This invention relates to a booster, provided with a power piston which is operated by fluid pressure, for boosting input force applied to an input member in order to output the same force after having boosted.
This type booster has been widely used in the brake operation mechanism in the vehicles or the like for the purpose of increasing the output force without increasing the input stroke. In the conventional boosters the input stroke is generally made equal in its amount to the output stroke (the input stroke is larger, to be more exact, than the output stroke by the amount of its idle stroke), which is liable to make the input stroke uselessly large, being an inevitable weak point.
Assuming a case wherein a mechanism under observation is a vehicle hydraulic brake, it is required that fluid (oil) consumption due to initial stage elastic deformation of each component member of the hydraulic system such as piston cup should be compensated, to say nothing of the requirement of eliminating the brake clearance, during the time from starting of the piston movement in the master cylinder to starting of the close sliding of the brake shoe or brake pad onto the brake drum or brake disc. For that reason, the piston of the master cylinder must be moved for a considerably long distance. During the initial stroke stage the brake effect is scarecely produced, so the brake feeling to the driver won't be deteriorated even if the input stroke and the output stroke of a booster, which is to be disposed between the brake pedal and the master cylinder, are not in a proportional relationship. There is, therefore, no problem even if the piston of the master cylinder is shifted, during the initial stroke stage, independently of the operation amount of the brake pedal by the driver, provided that the operation amount of the brake pedal comes into proportional relationship with the shift amount of the master cylinder after the starting of the sliding of the brake shoe or brake pad with the drum or disc. It is not a requisite that the input and output stroke of the booster should be identical during the entire operation range, as conventionally has been so believed.